PSU for i7@3.6 + 6990

You should need about 700W for that setup. Xigmatek's aren't bad, but it probably can't output that much on the 12V rail. An 850W that can reliably do 700W or 58A should be fine.

Hey man, thanks for your input. In regards to the Toughpower XT 875w, the Thermaltake website states:

"24/7 @ 50 °C: Guaranteed to deliver 575W / 675W / 775W / 875W continuous output power." & "12Vin1: single +12V rail design providing up to 48A / 56A / 64A / 72A."

So, should be fine, yeah?

I'm just a bit worried because if the whole PC is restarting itself with a 750w PSU while the 6990 is at stock clock speeds, adding only another 125w of power (750w-875w) would seem to be cutting it pretty fine...

The 6990 won't use 475 watts by itself.. That's a measure of the total system power consumption.. So basically, a good 650W PSU will suffice.. On that note, the Xigmatech PSU should be enough provided it can truly deliver those advertised 700 watts of power.. As for restarting, the problem could be elsewhere also (although I agree its the PSU which needs to be checked first qheneveg such problems arise).. Could be caused due to heat building up inside your PC case.. Could you please give your full system specs..!!

No problemo:

Asus P6T deluxe v1
i7-920 @ 3.6
6Gb 1333 Corsair RAM
Powercolour 6990
2 x 1Tb WD HDD
Xigmatek 750w PSU

Previously (with both a 4670 & 5870) the primary PCIE slot was only running at 8x (as demonstrated by both CPUZ and Catalyst), when it should only ever run at 16x. I thought there was something wrong with the PCIE slot, but the memory bandwidth appeared normal so I never worried about it. With the 6990 both programs demonstrate the slot's running at 16x with normal memory bandwidth, so I don't think there's an issue there.

Never had a problem with the 5870: no spontaneous shut-downs like with the 6990. The 6990 won't play BC2 or Shogan2 for more than 5 seconds before the entire PC restarts, but it will play CS:S (@250-300fps, lol) comfortably. The 6990 will also play VLC fine, just no demanding games... power problem, yeah? Any experiments you'd recommend?

Their 775W unit should be enough, but you won't harm anything by getting the 875W.

In regards to heat, I have an Antec 900 case, which is kinda small but well ventilated. There're two fans at the front and I've turned one around, right in front of the 6990, to draw heat straight out of the case. I'm pretty sure heat isn't the problem.

turn that fan back round m8 your not helping airflow as the top fan is so big it causes a negative atmosphere inside the case even with both front fans at full.

i also have a tough power (850w) and have no issues with it at all. add to that it has a 5 year warranty.

hey man, thanks for your advice. the front fan (1 of 2) is right in front of the 6990, contained within a hdd bay. surely it can't hurt to have the hot air from the 6990 being sucked directly out of the case. the other fan at the front (below) is sucking air in over the hard drives. i'm a bit paranoid about heat cause i've only got a stock cpu cooler and the case is small.

i'm thinking about resetting my bios and seeing how the 6990 goes at load. this may help me identify the problem, whether it's really down to the psu... ??

I 2nd this suggestion!

Both those fans should be intake or else some of the exhausted heat will be pulled back into the machine by the other fan, that's a bad idea!

You're also creating turbulence inside the machine that disrupts the airflow, a side fan right at the GPU exhausting air would be better than reversing one of the front intake fans.

IMO, the Antec 900 is not an ideal case for high end (or should I say high heat dissipating) hardware.. You turning the intake fan as exhaust is further worsening the case.. I won't get into technicalities as it has been already explained by Hexit.. So just return the fan to its default status and you will definitely see improvements..

ok, i've reset the mobo bios back to default (no OC) and i'm getting about 30 seconds game time in BC2 now, as opposed to the 5-10 seconds i was getting previously. so, definately a power issue...

I've reset the mobo bios to default, so the cpu's no longer overclocked. i've tried Blops, Bulletstorm, Civ5, CS:S, DoD, Forged Alliance, Fallout New Vegas, and Dead Rising 2 without a problem. No crashes, no PC restarts.

However, the two games I play most, BC2 and Shogun 2 both crash after 30 seconds – 1 minute of gameplay. This is an improvement on the 5-10 seconds prior to reseting the mobo bios.

Seems like a power issue, but why only with these two games?

replaced crappy xigmatek 750w psu with a thermaltake toughpower 1200w. problem solved. thanks everyone for your input.